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Cygwin: shm: Convert muto into SRWLOCK and avoid overlocking 

shmat may call shmget.  shmget locks by itself as necessary,
so there's no reason to keep the lock active and recurse into
the lock.  Use SRWLOCK and only lock  as required.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2022-08-22 14:28:11 +02:00
parent 2e03e5a040
commit d6c50e630a
1 changed files with 10 additions and 10 deletions
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20
winsup/cygwin/shm.cc
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@ -113,9 +113,9 @@ struct shm_attached_list {
static SLIST_HEAD (, shm_attached_list) sph_list;
static NO_COPY muto shm_guard;
#define SLIST_LOCK() (shm_guard.init ("shm_guard")->acquire ())
#define SLIST_UNLOCK() (shm_guard.release ())
static NO_COPY SRWLOCK shm_lock = SRWLOCK_INIT;
#define SLIST_LOCK() (AcquireSRWLockExclusive (&shm_lock))
#define SLIST_UNLOCK() (ReleaseSRWLockExclusive (&shm_lock))
int
fixup_shms_after_fork ()
@ -174,22 +174,22 @@ shmat (int shmid, const void *shmaddr, int shmflg)
shmid if one exists. Since shmctl inserts a new entry for this
shmid into ssh_list automatically, we just have to go through
that list again. If that still fails, well, bad luck. */
SLIST_UNLOCK ();
if (shmid && shmget ((key_t) shmid, 0, IPC_KEY_IS_SHMID) != -1)
{
SLIST_LOCK ();
SLIST_FOREACH (ssh_entry, &ssh_list, ssh_next)
{
if (ssh_entry->shmid == shmid)
break;
goto inc_ref_count;
}
}
if (!ssh_entry)
{
/* Invalid shmid */
set_errno (EINVAL);
SLIST_UNLOCK ();
return (void *) -1;
}
/* Invalid shmid */
set_errno (EINVAL);
return (void *) -1;
}
inc_ref_count:
/* Early increment ref counter. This allows further actions to run with
unlocked lists, because shmdt or shmctl(IPC_RMID) won't delete this
ssh_entry. */